The major part of synthetic thickening agents consist of polymers and copolymers capable of acting as thickening agents following a partial or total neutralization.
In these cases, the low solubility or the insolubility in water of the non-neutralized polymer are made use of, thus allowing to obtain solutions or dispersions of the polymer in relatively high concentrations and of sufficiently low viscosities. This permits the use and the dosage of the thickening agent until the time of the neutralization thereof.
Polymer systems behaving like this have been known for a long time and they are in various physical forms which are more or less easy to use.
Thickening agents in aqueous solutions are known, e. g. some non cross-linked poly(meth)acrylic acids which, however, are rather difficult to use due to the high viscosity thereof, and moreover are not very effective.
Powdered thickening agents are also known, for example, cross-linked poly(meth)acrylic acids described in U.S. Pat. No. 2,798,053.
These products are very effective, but they are used more and more seldom as they cannot meet the current technological requirements since, to use them it is necessary to prepare an aqueous dispersion of the acidic form to use in the thickening process. The step of dispersion of the acidic form is very laborious and lengthy, moreover the obtained thickening agents are not resistant to salts.
Effective and easy to use polymer thickening agents are the copolymers in aqueous emulsion or polymer latexes, as those described in the UK Patent 870,994. They are copolymers of methacrylic acid with alkyl (C.sub.1 -C.sub.4) acrylates, optionally cross-linked, obtained with emulsion polymerization techniques. According to these methods, poorly viscous latexes can be obtained, the active content of which ranges from 25 to 50% by weight.
Nevertheless, the salt resistance of these products is still insufficient.
Polymer systems, preferably in the form of latex, which are a further advance in terms of effectiveness and salt resistance while being easy to handle are those described in EP-A- 0,013,836 and European Patents 0,0110806 and 0,109,820. These publications claim copolymers obtained from monomeric mixtures similar to those described in the already cited UK Patent 870,994 in which, however, novel comonomers are present having a particular structure, such as (meth)acrylates or itaconates of non-ionic surfactants, such as ethoxylated fatty alcohols or ethoxylated alkylphenols.
These thickening agents are widely used in the textile, detergent and cosmetic fields.
Particularly important is the use of the latter thickening agents in latex form as additives to adjust, increasing it, the final viscosity of pastes for pigment printing of textiles.
A technological problem in printing textiles, in particular mixed synthetic fiber/cotton textiles, such as polyester/cotton, arises from the colour rendering of the paste and the dye fastness and contour sharpness of the printed design ("bleeding" effect).